Communication support for low capability devices

ABSTRACT

A method for receiving downlink control information is provided. The method includes receiving configuration information comprising a bit-map corresponding to a set of time occasions that are separated by a same interval; identifying at least one time occasion to monitor a candidate physical downlink control channel (PDCCH) on at least one search space; and decoding the candidate PDCCH in the identified at least one time occasion for obtaining the downlink control information.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 16/201,615, which was filed in the U.S. Patent andTrademark Office on Nov. 27, 2018, which is a continuation of U.S.patent application Ser. No. 15/812,659, which was filed in the U.S.Patent and Trademark Office on Nov. 14, 2017, now U.S. Pat. No.10,142,933, issued on Nov. 27, 2018, which is a continuation of U.S.patent application Ser. No. 15/397,181, which was filed in the U.S.Patent and Trademark Office on Jan. 3, 2017, which is a continuation ofU.S. patent application Ser. No. 14/861,596, which was filed in the U.S.Patent and Trademark Office on Sep. 22, 2015, now U.S. Pat. No.9,538,521, issued on Jan. 3, 2017, which is a continuation of U.S.patent application Ser. No. 13/715,174, which was filed in the U.S.Patent and Trademark Office on Dec. 14, 2012, now U.S. Pat. No.9,144,065, issued on Sep. 22, 2015, which claims priority under 35U.S.C. § 119(e) to U.S. Provisional Patent Application No. 61/576,695,which was filed in the U.S. Patent and Trademark Office on Dec. 16,2011, the content of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to wireless communicationsystems and, more particularly, to the transmission and reception ofcontrol channels and data channels to and from, respectively, UEs withlimited capabilities.

2. Description of the Art

A communication system includes a DownLink (DL) that conveystransmission signals from transmission points such as Base Stations(BSs) (which may also be referred to as NodeBs) to User Equipments (UEs)and an UpLink (UL) that conveys transmission signals from UEs toreception points such as NodeBs. A UE, also commonly referred to as aterminal or a mobile station, may be fixed or mobile, and may be adevice such as a cellular phone, a personal computer device, etc. ANodeB, which is generally a fixed station, may also be referred to as anaccess point or other equivalent terminology.

DL signals include data signals, which carry information content,control signals, and Reference Signals (RSs), which are also known aspilot signals. A NodeB conveys data information to UEs throughrespective Physical Downlink Shared CHannels (PDSCHs) and controlinformation through respective Physical Downlink Control CHannels(PDCCHs). Multiple RS types may be supported, such as a Common RS (CRS)transmitted over substantially the entire DL BandWidth (BW) and theDeModulation RS (DMRS) transmitted in a same BW as an associated PDSCH.

UL signals also include data signals, control signals, and RSs. UEsconvey data information to NodeBs through respective Physical UplinkShared CHannels (PUSCHs) and control information through respectivePhysical Uplink Control CHannels (PUCCHs). A UE transmitting datainformation may also convey control information through a PUSCH. The RSmay be a DMRS or a Sounding RS (SRS), which a UE may transmitindependently of a PUSCH.

Downlink Control Information (DCI) serves several purposes, and isconveyed through DCI formats in respective PDCCHs. For example, DCIincludes DL Scheduling Assignments (SAs) for PDSCH reception and UL SAsfor PUSCH transmissions. As PDCCHs are a major part of a total DLoverhead, the resources required to transmit PDCCHs directly reduce DLthroughput. One method for reducing PDCCH overhead is to scale it's thesize of the overhead according to the resources required to transmit theDCI formats during a DL Transmission Time Interval (TTI). WhenOrthogonal Frequency Division Multiple (OFDM) is used as a DLtransmission method, a Control Channel Format Indicator (CCFI) parametertransmitted through a Physical Control Format Indicator CHannel (PCFICH)can be used to indicate a number of OFDM symbols occupied by PDCCHs in aDL TTI.

FIG. 1 is a diagram illustrating a conventional structure for PDCCHtransmissions in a DL TTI.

Referring to FIG. 1, a DL TTI includes one subframe having a number N ofOFDM symbols. In the present example, N=14. A DL control region thatincludes PDCCH transmissions occupies a first M OFDM symbols 110. Aremaining N−M OFDM symbols are used primarily for PDSCH transmissions120. A PCFICH 130 is transmitted in some sub-carriers, also referred toas Resource Elements (REs), of a first OFDM symbol and includes 2 bitsindicating a DL control region size of M=1, or M=2, or M=3 OFDM symbols.Moreover, some OFDM symbols also contain respective RS REs 140 and 150.These RSs 140 and 150 are transmitted substantially over an entire DLoperating BandWidth (BW), and are referred to as Common RSs (CRSs), asthey can be used by each UE to obtain a channel estimate for its DLchannel medium and to perform other measurements. The BW unit for aPDSCH or a PUSCH over a subframe is referred to as a Physical ResourceBlock (PRB). A PRB includes several REs, such as 12 Res, for example.

A PDCCH and a PCFICH transmitted with the conventional structure in FIG.1 are referred to as C-PDCCH and a C-PCFICH, respectively. Additionalcontrol channels may be transmitted in a DL control region but are notshown for brevity. For example, when using a Hybrid Automatic RepeatreQuest (HARQ) process for a transmission of data Transport Blocks (TBs)in a PUSCH, a NodeB may transmit HARQ-ACKnowledgement (ACK) informationin a Physical Hybrid-HARQ Indicator CHannel (PHICH) to indicate to a UEwhether its previous transmission of each data Transport Block (TB) in aPUSCH was correctly received (i.e., through an ACK) or incorrectlyreceived (i.e., through a Negative ACK (NACK)). A PHICH transmitted witha conventional structure is referred to as C-PHICH. The aforementionedconventional DL control channels will be jointly referred to as C-CCHs.

FIG. 2 is a diagram illustrating a conventional encoding andtransmission process for a DCI format.

Referring to FIG. 2, a NodeB separately codes and transmits each DCIformat in a respective PDCCH. A Radio Network Temporary Identifier(RNTI) for a UE, for which a DCI format is intended for, masks a CyclicRedundancy Check (CRC) of a DCI format codeword in order to enable theUE to identify that a particular DCI format is intended for the UE. TheCRC of (non-coded) DCI format bits 210 is computed using a CRCcomputation operation 220, and the CRC is then masked using an exclusiveOR (XOR) operation 230 between CRC and RNTI bits 240. The XOR operation230 is defined as: XOR(0,0)=0, XOR(0,1)=1, XOR(1,0)=1, XOR(1,1)=0. Themasked CRC bits are appended to DCI format information bits using a CRCappend operation 250, channel coding is performed using a channel codingoperation 260 (e.g. an operation using a convolutional code), followedby rate matching operation 270 applied to allocated resources, andfinally, an interleaving and a modulation 280 operation are performed,and the output control signal 290 is transmitted. In the presentexample, both a CRC and a RNTI include 16 bits.

FIG. 3 is a diagram illustrating a conventional reception and decodingprocess for a DCI format.

Referring to FIG. 3, a UE receiver performs a reverse of the operationsperformed by the NodeB transmitter in order to determine whether the UEhas a DCI format assignment in a DL subframe. A received control signal310 is demodulated and the resulting bits are de-interleaved atoperation 320, a rate matching applied at a NodeB transmitter isrestored through operation 330, and data is subsequently decoded atoperation 440. After decoding the data, DCI format information bits 360are obtained after extracting CRC bits 350, which are then de-masked 370by applying the XOR operation with a UE RNTI 380. Finally, a UE performsa CRC test 390. If the CRC test passes, a UE determines that a DCIformat corresponding to the received control signal 310 is valid anddetermines parameters for signal reception or signal transmission. Ifthe CRC test does not pass, a UE disregards the presumed DCI format.

The DCI format information bits correspond to several InformationElements (IEs) such as, for example, the Resource Allocation (RA) IEindicating the part of the DL BW or UL BW allocated to a UE for PDSCHreception or PUSCH transmission, respectively, the Modulation and CodingScheme (MCS) IE indicating the data MCS, the Transmission Power Control(TPC) IE indicating an adjustment to the PUSCH transmission power or tothe HARQ-ACK signal transmission power in a PUCCH, the New DataIndicator (NDI) IE informing a UE whether the scheduled data TBcorresponds to a new transmission or to a retransmission for the sameHARQ process, and so on.

In order to avoid a C-PDCCH transmission to a UE that blocks a C-PDCCHtransmission to another UE, a location of each C-PDCCH in thetime-frequency domain of a DL control region is not unique. Therefore, aUE may perform multiple decoding operations per DL subframe to determinewhether there are any C-PDCCHs intended for the UE in a DL subframe. TheREs carrying a PDCCH are grouped into Control Channel Elements (CCEs) inthe logical domain. For a given number of DCI format bits in FIG. 2, anumber of CCEs for a respective C-PDCCH depends on a channel coding rate(Quadrature Phase Shift Keying (QPSK) is the modulation scheme in thepresent example). A NodeB may use a lower channel coding rate (i.e.,more CCEs) for transmitting PDCCHs to UEs experiencing a low DLSignal-to-Interference and Noise Ratio (SINR) than to UEs experiencing ahigh DL SINR. The CCE aggregation levels may include, for example, 1, 2,4, and 8 CCEs.

For a C-PDCCH decoding process, a UE may determine a search space forcandidate C-PDCCH transmissions after the UE restores the CCEs in thelogical domain according to a common set of CCEs for all UEs (i.e., aCommon Search Space (CSS)) and according to a UE-dedicated set of CCEs(i.e., a UE-Dedicated Search Space (UE-DSS)). A CSS may include thefirst C CCEs in the logical domain. A UE-DSS may be determined accordingto a pseudo-random function having UE-common parameters as inputs, suchas the subframe number or the total number of CCEs in the subframe, andUE-specific parameters such as the RNTI. For example, for CCEaggregation levels L∈{1,2,4,8}, the CCEs corresponding to PDCCHcandidate m are given by Equation (1)CCEs for C-PDCCH candidate m=L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i.  (1)

In Equation (1), N_(CCE,k) is the total number of CCEs in subframe k,i=0, . . . , L−1, m=0, . . . , M_(C) ^((L))−1, and M_(C) ^((L)) is thenumber of C-PDCCH candidates to monitor in the search space. Exemplaryvalues of M_(C) ^((L)) for L∈{1,2,4,8} are, respectively, {6, 6, 2, 2}.For the UE-CSS, Y_(k)=0. For the UE-DSS, Y_(k)=(A·Y_(k-1))mod D, whereY⁻¹=UE_RNTI≠0, A=39827, and D=65537.

DCI formats conveying information to multiple UEs are transmitted in aCSS. Additionally, if enough CCEs remain after the transmission of DCIformats conveying information to multiple UEs, a CSS may also conveysome DCI formats for PDSCH reception or PUSCH transmission. A UE-DSSexclusively conveys DCI formats for PDSCH reception or PUSCHtransmission. For example, a CSS may include 16 CCEs and support 2 DCIformats with L=8 CCEs, or 4 DCI formats with L=4 CCEs, or 1 DCI formatwith L=8 CCEs and 2 DCI formats with L=4 CCEs. The CCEs for a CSS areplaced first in the logical domain (prior to interleaving).

FIG. 4 is a diagram illustrating a conventional transmission process ofa DCI format in a respective C-PDCCH.

Referring to FIG. 4, after channel coding and rate matching areperformed (as described with reference to FIG. 2), encoded DCI formatbits are mapped to C-PDCCH CCEs in the logical domain. The first 4 CCEs(L=4), CCE1 401, CCE2 402, CCE3 403, and CCE4 404 are used for C-PDCCHtransmission to UE1. The next 2 CCEs (L=2), CCE5 411 and CCE6 412, areused for C-PDCCH transmission to UE2. The next 2 CCEs (L=2), CCE7 421and CCE8 422, are used for C-PDCCH transmission to UE3. Finally, thelast CCE (L=1), CCE9 431, is used for C-PDCCH transmission to UE4.

The DCI format bits are then scrambled, at step 440, by a binaryscrambling code, and the scrambled bits are modulated at step 450. EachCCE is further divided into Resource Element Groups (REGs). For example,a CCE including 36 REs can be divided into 9 REGs, such that each REGincludes 4 REs. In step 460, interleaving is applied among REGs inblocks of four QPSK symbols. For example, a block interleaver may beused where interleaving is performed on symbol-quadruplets (i.e., fourQPSK symbols corresponding to the four REs of a REG) instead of onindividual bits. After interleaving the REGs, in step 470, a resultingseries of QPSK symbols may be shifted by J symbols, and finally, in step480, each QPSK symbol is mapped to an RE in a DL control region.Therefore, in addition to RSs from NodeB transmitter antennas 491 and492, and other control channels, such as a PCFICH 493 and a PHICH (notshown), REs in a DL control region contain QPSK symbols for PDCCHscorresponding to DCI formats for UE1 494, UE2 495, UE3 496, and UE4 497.

The C-PDCCH structure in FIG. 4 uses a maximum of M=3 OFDM symbols andtransmits the signal substantially over a total DL BW. As a consequenceof using such a structure, such a control region has a limited capacity,and therefore cannot achieve interference coordination in the frequencydomain. There are several cases where expanded capacity or interferencecoordination in the frequency domain is needed for transmission ofcontrol signals. One such case is the extensive use of spatialmultiplexing for PDSCH transmissions, where multiple DL SAs correspondto the same PDSCH resources. Another case is for heterogeneous networkswhere DL transmissions in a first cell experience strong interferencefrom DL transmissions in a second cell and DL interference coordinationin the frequency domain between the two cells is needed.

Due to REG-based transmission and interleaving of C-PDCCHs, the controlregion cannot be expanded to include more OFDM symbols while maintainingcompatible operation with existing UEs that cannot be aware of such anexpansion. An alternative to the REG-based transmission and interleavingof C-PDCCHs is to extend the control region in the PDSCH region and useindividual PRBs for transmitting new PDCCHs, which are referred to asEnhanced PDCCHs (E-PCCCHs).

FIG. 5 is a diagram illustrating a conventional E-PDCCH transmissionstructure.

Referring to FIG. 5, although E-PDCCH transmissions start immediatelyafter C-PDCCH transmissions 510 and are transmitted over all remainingDL subframe symbols, they may instead always start at a fixed location,such as the fourth OFDM symbol. E-PDCCH transmissions occur in fourPRBs, 620, 630, 640, and 650, while remaining PRBs 660, 662, 664, 666,668 are used for PDSCH transmissions. As an E-PDCCH transmission over agiven number of subframe symbols may require fewer REs than the numberof subframe symbols available in a PRB, multiple E-PDCCHs may bemultiplexed in a same PRB. The multiplexing can be in any combination ofpossible domains (i.e., time domain, frequency domain, or spatialdomain) and, in a manner similar to a PDCCH, an E-PDCCH includes atleast one Enhanced CCE (E-CCE).

A transmission for an extended control channel (E-PDCCH, E-PCFICH,E-PHICH) may be in a same PRB, in which case the transmission isreferred to as localized, or over multiple PRBs, in which case thetransmission is referred to as distributed. The aforementioned EnhancedControl CHannels are jointly referred to as E-CCHs. The demodulation ofinformation in an E-CCH may be based on a CRS or on a DMRS.

FIG. 6 is a diagram illustrating a conventional DMRS structure.

Referring to FIG. 6, DMRS REs 610 are placed in some OFDM symbols of aPRB. When there are two NodeB transmitter antenna ports, a first DMRStransmission is assumed to apply the Orthogonal Covering Code (OCC) of{1, 1} over two DMRS REs that are located in a same frequency positionand are successive in the time domain while a second DMRS transmissionis assumed to apply the OCC of {1, −1}. A UE receiver can estimate thechannel experienced by the signal from each NodeB transmitter antennaport by removing a respective OCC.

UL Control Information (UCI) is transmitted from a UE to a NodeB tofacilitate PDSCH transmissions or PUSCH transmissions. UCI includesHARQ-ACK information associated with a transmission of one or moreTransport Blocks (TBs) in a PDSCH, Channel State Information (CSI)informing a NodeB about a channel experienced by DL transmissions to aUE, and Service Request (SR) informing a NodeB that a UE has data totransmit. CSI may include a Channel Quality Indicator (CQI), whichimplicitly or explicitly informs a NodeB of a wideband or a sub-bandSINR experienced by a UE, a Precoding Matrix Indicator (PMI), whichinforms of an entry in a precoding matrix for a NodeB to applybeamforming to a DL signal transmission, or a Rank Indicator (RI) whichinforms a NodeB that a UE can support spatial multiplexing for a DLsignal transmission.

FIG. 7 is a diagram illustrating a conventional structure for a HARQ-ACKsignal transmission in one of the two subframe slots of a PUCCH.

Referring to FIG. 7, HARQ-ACK signals and RS that enable coherentdemodulation of HARQ-ACK signals are transmitted in one slot 710 of aPUCCH subframe including 2 slots. The transmission in the other slot canbe at a different part of the UL BW. HARQ-ACK information bits 720modulate 730 a Zadoff-Chu (ZC) sequence 740, for example using BinaryPhase Shift Keying (BPSK) for 1 HARQ-ACK bit or QPSK for 2 HARQ-ACKbits, which is then transmitted after performing a Inverse Fast FourierTransform (IFFT) operation 750. Each RS 760 is transmitted using anunmodulated ZC sequence.

For a UL system BW including N_(RB) ^(max,UL) RBs, where each RBincludes N_(sc) ^(RB)=12 REs, a ZC sequence r_(u,v) ^((α))(n) can bedefined by a Cyclic Shift (CS) α of a base ZC sequence r _(u,v)(n)according to r_(u,v) ^((α))(n)=e^(jαn) r _(u,v)(n), 0≤n<M_(sc) ^(RS),where M_(sc) ^(RS)=mN_(sc) ^(RB) is a length of the ZC sequence,1≤m≤N_(RB) ^(max,UL), and r _(u,v)(n)=x_(q)(n mod N_(ZC) ^(RS)) where aq^(th) root ZC sequence is defined by

${{x_{q}(m)} = {\exp\left( \frac{{- j}\;\pi\;{{qm}\left( {m + 1} \right)}}{N_{ZC}^{RS}} \right)}},$0≤m≤N_(ZC) ^(RS)−1 with q given by q=└q+½┘+v·(−1)^(└2q┘) and q given byq=N_(ZC) ^(RS)·(u+1)/31. A length N_(ZC) ^(RS) of a ZC sequence is givenby a largest prime number such that N_(ZC) ^(RS)<M_(sc) ^(RS). MultipleRS sequences can be defined from a single base sequence throughdifferent values of α. A PUCCH transmission is assumed to be in one RB(M_(sc) ^(RS)=N_(sc) ^(RB)).

FIG. 8 is a diagram illustrating a conventional structure for a periodicCSI signal transmission in one of the two subframe slots of a PUCCH.

Referring to FIG. 8, CSI signals and RSs that enable coherentdemodulation of CSI signals are transmitted in one slot 810 of a PUCCHsubframe including 2 slots. The transmission in the other slot can be ata different part of the UL BW. After encoding (using for example a blockcode) and modulation (using for example QPSK) which are not shown forbrevity, encoded CSI bits 820 modulate 830 a ZC sequence 840 which isthen transmitted after performing an IFFT operation 840. Each RS 850 istransmitted using an unmodulated ZC sequence.

FIG. 9 is a diagram illustrating a transmitter for a ZC sequence forwhich, without modulation, serves as an RS and with modulation serves asa HARQ-ACK signal or as a CSI signal.

Referring to FIG. 9, a mapper 920 maps a ZC sequence 910 to REs of anassigned transmission BW as they are indicated by RE selection unit 925.Subsequently, an IFFT is performed by IFFT unit 930, a CS is applied tothe output by CS unit 940, followed by scrambling with a cell-specificsequence using scrambler 950, a Cyclic Prefix (CP) is inserted by CPinsertion unit 960, and the resulting signal is filtered by filter 970.Finally, a transmission power P_(PUCCH) is applied by power amplifier980 and a ZC sequence is transmitted 990. The reverse of theseoperations is performed at a NodeB receiver.

Different CSs of a ZC sequence provide orthogonal ZC sequences.Therefore, different CSs α of a same ZC sequence can be allocated todifferent UEs in a same PUCCH RB and achieve orthogonal multiplexing forHARQ-ACK signals and RS or for CSI signals and RS. For a RB includingN_(sc) ^(RB)=12 REs, there are 12 different CSs. A number of usable CSsdepends on the channel dispersion characteristics, and can typicallyrange between 3 and 12 CSs. Orthogonal multiplexing can also be in thetime domain using OCC where PUCCH symbols conveying a same signal typein each slot are multiplied with elements of an OCC. For example, forthe structure in FIG. 7, a HARQ-ACK signal transmission can be modulatedby a length-4 OCC, such as a Walsh-Hadamard (WH) OCC, while an RStransmission can be modulated by a length-3 OCC, such as a DFT OCC. Inthis manner, the multiplexing capacity is increased by a factor of 3(determined by the OCC with the smaller length N_(oc)).

UEs may communicate over a total system BW or over only a part of thesystem BW. The former UEs can benefit from most or all networkcapabilities for PDSCH receptions or PUSCH transmissions, are typicallyused by humans, and are referred to as conventional UEs herein. Thelatter UEs have substantially reduced capabilities compared to theformer UEs in order to substantially reduce their cost, are typicallyassociated with machines, and are referred to as Machine TypeCommunication (MTC) UEs herein.

MTC UEs are low cost devices targeting various low data rate trafficapplications including smart metering, intelligent transport systems,consumer electronics, and medical devices. Typical traffic patterns fromMTC UEs are characterized by low duty cycles and small data packets inthe order of a few tens or a few hundred bytes. MTC UEs have typicallylow mobility, but high mobility MTCs, such as in motor vehicles, forexample, may also exist. Also, unlike conventional UEs, MTC UEs generatemore UL than DL traffic and a majority of DL traffic is higher layercontrol information, such as Radio Resource Control (RRC) information,for configuration of a communication with a NodeB.

Unlike conventional UEs, such as for example a smart-phone, which mayhave many features, MTC UEs only have a minimum of necessary features,and the modem is a primary contributor to the cost of an MTC UE.Therefore, main cost drivers for MTC UEs are Radio Frequency (RF)components and Digital Base-Band (DBB) components mainly for thereceiver. RF components include the power amplifier, filters,transceiver radio chains, and possibly a duplexer (for full duplex FDDoperation). DBB components include a channel estimator, a channelequalizer, a PDCCH decoder, a PDSCH decoder, and a subframe buffer. Forexample, a channel estimator may be based on a Minimum Mean Square Error(MMSE) estimator, a channel equalizer may be an FFT, a PDCCH decoder maybe a decoder for a Tail Biting Convolutional Code (TBCC), and the datadecoder may be a decoder for a Turbo Code (TC) or a TBCC.

RF costs are related to implementation and production methods as well asto design choices. For example, considering economies of scale, it maybe more cost effective to use the same amplifier for conventional UEsand MTC UEs, which will also ensure a same UL coverage, while the numberof transmitter antennas for MTC UEs may be limited to one antenna.

DBB costs are related to the communication capabilities of MTC UEs andare dominated by the receiver complexity, which is typically about anorder of magnitude larger than the transmitter complexity. As thechannel estimator complexity, the FFT complexity and the subframebuffering requirements are directly associated to the reception BW, DLtransmissions to MTC UEs may be over a smaller BW than DL transmissionsto conventional UEs. For example, DL transmissions to MTC UEs may beover a 1.4 MHz BW while DL transmissions to conventional UEs may be overa 20 MHz BW.

A complexity of a PDCCH decoder depends on a number of decodingoperations an MTC UE needs to perform per DL subframe. As MTC UEs do notneed to support a same number of transmission modes (TMs) asconventional UEs, for example MTC UEs may not need to support spatialmultiplexing for PDSCH or for PUSCH, a maximum number of decodingoperations per DL subframe can be significantly smaller than that forconventional UEs. A complexity of a PDSCH decoder depends on a maximumsupportable data rate. Allowing for a relatively small maximum data ratefor MTC UEs provides a limit to an associated decoder complexity.

MTC UEs generally access the communication system in the same manner asconventional UEs. Synchronization signals are first acquired toestablish synchronization with a NodeB followed by a detection of aBroadcast CHannel (BCH) that conveys essential information forsubsequent communication between a NodeB and UEs (conventional or MTCones). Regardless of a DL BW, synchronization signals and BCH aretransmitted over a minimum DL BW located in the center of a DL BW, suchas in the middle six RBs of a DL BW, and over a number of OFDM symbolsin a subframe, for example. After establishing communication with aNodeB, a different part of a DL BW may be allocated to an MTC UE.

One aspect of supporting communication of MTC UEs is a design of DLcontrol signaling. As transmissions of C-CCHs are distributedsubstantially over a total DL system BW, if MTC UEs receive DLtransmissions only in a BW smaller than the total BW, the MTC UEs maynot be able to decode C-CCHs. The use of E-CCHs can provide DL controlsignaling support for MTC UEs, but due to reduced receiver DBBcapabilities of MTC UEs, it may not be possible to use a same design ofE-CCHs for MTC UEs and for conventional UEs.

Another aspect of supporting communication of MTC UEs is a reduction inan overhead associated with DL control signaling and UL controlsignaling for MTC UEs. As data TBs associated with MTC UEs are typicallysubstantially smaller than the ones associated with conventional UEs,applying same DL or UL control or data multiplexing mechanisms for MTCUEs as for conventional UEs will cause resource utilization for MTC UEsto be substantially worse than the resource utilization for conventionalUEs.

Another aspect of supporting communication of MTC UEs is applying a setof functionalities associated with signal transmissions to or from MTCUEs. If signal transmissions for MTC UEs are over a smaller BW than forconventional UEs, different functionalities can be often needed for MTCUEs compared to conventional UEs. Higher power utilization can also bedesirable for MTC UEs.

Therefore, there is a need to design control signaling and data orcontrol multiplexing for MTC UEs.

There is also a need to reduce control overhead for MTC UEs.

There is also a need to define, whenever necessary, differentfunctionalities for signal transmissions to or from MTC UEs compared toconventional UEs and to increase power savings for MTC UEs.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the present invention is to address at leastthe aforementioned limitations and problems and provide at least theadvantages described below. An aspect of the present invention providesmethods and apparatus for a UE with reduced capabilities (MTC UE) totransmit and receive signaling and to conserve power in a network thatalso supports conventional UEs.

According to an aspect of the present invention, a method for receivingdownlink control information is provided. The method includes receivingconfiguration information comprising a bit-map corresponding to a set oftime occasions that are separated by a same interval; identifying atleast one time occasion to monitor a candidate PDCCH on at least onesearch space; and decoding the candidate PDCCH in the identified atleast one time occasion for obtaining the downlink control information.

According to another aspect of the present invention, an apparatus of auser equipment for receiving downlink control information is provided.The apparatus includes a receiver configured to receive configurationinformation comprising a bit-map corresponding to a set of timeoccasions that are separated by a same interval; and a processorconfigured to identify at least one time occasion to monitor a candidatePDCCH on at least one search space, and decode the candidate PDCCH inthe identified at least one time occasion for obtaining the downlinkcontrol information.

According to another aspect of the present invention, a method fortransmitting downlink control information is provided. The methodincludes transmitting, to a user equipment, configuration informationcomprising a bit-map corresponding to a set of time occasions that areseparated by a same interval; identifying at least one time occasion inwhich the user equipment monitors a set of candidate PDCCHs on at leastone search space; and transmitting downlink control information on acandidate PDCCH of the set of candidate PDCCHs within the identified atleast one time occasion.

According to another aspect of the present invention, an apparatus of abase station for transmitting downlink control is provided. Theapparatus includes a transmitter configured to transmit, to a userequipment, configuration information comprising a bit-map correspondingto a set of time occasions that are separated by a same interval; and aprocessor configured to identify at least one time occasion in which theuser equipment monitors a set of candidate PDCCHs on at least one searchspace, and control the transmitter to transmit downlink controlinformation on a candidate PDCCH of the set of candidate PDCCHs withinthe identified at least one time occasion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional structure for PDCCHtransmissions in a DL TTI;

FIG. 2 is a diagram illustrating a conventional encoding andtransmission process for a DCI format;

FIG. 3 is a diagram illustrating a conventional reception and decodingprocess for a DCI format;

FIG. 4 is a diagram illustrating a conventional transmission process ofa DCI format in a respective C-PDCCH;

FIG. 5 is a diagram illustrating a conventional E-PDCCH transmissionstructure;

FIG. 6 is a diagram illustrating a conventional DMRS structure;

FIG. 7 is a diagram illustrating a conventional structure for a HARQ-ACKsignal transmission in one of the two subframe slots of a PUCCH;

FIG. 8 is a diagram illustrating a conventional structure for periodicCSI signal transmission in one of the two subframe slots of a PUCCH;

FIG. 9 is a diagram illustrating a conventional transmitter for a ZCsequence, which, without modulation, serves as an RS and with modulationserves as a HARQ-ACK signal or as a CSI signal;

FIG. 10 is a diagram illustrating a general principle of DL signaling toan MTC UE according to an embodiment of the present invention;

FIG. 11 is a diagram illustrating a multiplexing of CCHs, having a samestructure as C-CCHs, and PDSCHs for MTC UEs in OFDM symbols of a DLsubframe according to an embodiment of the present invention;

FIG. 12 is a diagram illustrating a multiplexing of E-CCHs and PDSCHsfor MTC UEs according to an embodiment of the present invention;

FIG. 13 is a diagram illustrating a multiplexing of PDSCHs and E-CCHsusing a granularity of a half PRB according to an embodiment of thepresent invention;

FIG. 14 is a diagram illustrating a CRS transmission only in a DL BWallocated to an MTC UE according to an embodiment of the presentinvention;

FIG. 15 is a diagram illustrating a first approach to increase amultiplexing capacity of periodic CQI transmissions from MTC UEsaccording to an embodiment of the present invention;

FIG. 16 is a diagram illustrating a second approach to increase amultiplexing capacity of periodic CSI transmissions from MTC UEsaccording to an embodiment of the present invention;

FIG. 17 is a diagram illustrating a third approach for increasing amultiplexing capacity of periodic CSI transmissions for MTC UEsaccording to an embodiment of the present invention;

FIG. 18 is a diagram illustrating a process for an MTC UE to perform SRStransmissions according to an embodiment of the present invention; and

FIG. 19 is a diagram illustrating a DL BW determination by an MTC UEafter BCH detection according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention are described hereinafterwith reference to the accompanying drawings. Throughout the drawings,the same drawing reference numerals may refer to the same or similarelements, features and structures. In the following description,specific details such as detailed configuration and components areprovided to assist the overall understanding of embodiments of thepresent invention. Therefore, it should be apparent to those skilled inthe art that various changes and modifications of the embodimentsdescribed herein can be made without departing from the scope and spiritof the invention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

Additionally, although embodiments of the present invention aredescribed herein with reference to Orthogonal Frequency DivisionMultiplexing (OFDM), embodiments of the present invention are also areapplicable to all Frequency Division Multiplexing (FDM) transmissions ingeneral and to Discrete Fourier Transform (DFT)-spread OFDM inparticular.

An embodiment of the invention that considers a DL control signalingdesign for MTC UEs is described as follows.

Higher layer signaling from a NodeB to an MTC UE may indicate that DLsignaling (for control or data) to the MTC UE begins at any OFDM symbolbetween a first OFDM symbol of a DL subframe and an OFDM symbol after amaximum number of OFDM symbols used for transmissions of C-CCHs. Inpractice, this is equivalent to a NodeB informing an MTC UE of a numberof OFDM symbols the MTC UE needs to assume as used for transmissions ofC-CCHs (regardless of whether there are transmissions of C-CCHs) toconventional UEs. Due to a reduced DL BW capability, an MTC UE cannotgenerally correctly decode C-CCHs transmitted over a wider DL BW andintended to conventional UEs, OFDM symbols conveying C-CCHs should bedismissed by MTC UEs. Therefore, DL signaling to MTC UEs may be in afraction of a DL subframe instead of being distributed over an entire DLsubframe as for conventional UEs.

A higher layer signaling indication to an MTC UE of a starting subframesymbol for DL signaling may also be a function of a DL subframe numberas certain DL subframes may convey different traffic types (for example,unicast or broadcast) and be associated with a different maximum numberof OFDM symbols for transmissions of C-CCHs. For example, in some DLsubframes this maximum number of OFDM symbols can be three, while inother subframes there is a maximum of two OFDM symbols. Although anumber of OFDM symbols used for transmitting C-CCHs is never zero, thisvalue may still be indicated to MTC UEs. It is up to a network to avoidtransmitting any C-CCHs to conventional UEs that do not need to be awareof this event. However, an MTC UE may need to exclude CRS REs from REsconveying DL signaling (control or data) as, unlike C-CCH REs, a NodeBcannot replace signaling of CRS with DL signaling to MTC UEs. Analternative to higher layer signaling is for MTC UEs to assume a maximumnumber of OFDM symbols for transmitting C-CCHs. However, in many cases,this assumption can be wasteful as transmissions of C-CCHs may requireless than a maximum number of OFDM symbols.

FIG. 10 is a diagram illustrating a general principle of DL signaling toan MTC UE according to an embodiment of the present invention.

Referring to FIG. 10, an MTC UE is informed, through higher layersignaling, of OFDM symbols available for DL signaling 1010 at a givensubframe (or the MTC UE may assume a maximum number of OFDM symbols fortransmissions of C-CCHs). OFDM symbols available for DL signaling to theMTC UE may or may not include all DL subframe symbols. The MTC UE isalso informed, through higher layer signaling, of a DL BW part allocatedfor DL signaling 1020. Different MTC UEs may be informed of differentparts of a DL BW, but all MTC UEs are informed of the same OFDM symbolsfor DL signaling. Therefore, higher layer signaling indicating OFDMsymbols for DL signaling may be common to all MTC UEs while higher layersignaling indicating a DL BW for DL signaling may be specific to eachMTC UE. Conventional UEs have all DL subframe symbols 1030 available andpotentially also have all DL BW (if there are no DL transmissions to MTCUEs) 1040 available, and the conventional UEs do not need be aware of apresence of MTC UEs.

After an MTC UE is informed of a number of OFDM symbols and of a DL BWpart for DL signaling, physical structures for transmissions of controlchannels and data channels need to be defined. A PDSCH transmission toan MTC UE can be the same as for a conventional UE and can occur over amaximum number of PRBs corresponding to an allocated DL BW part and to anumber of available OFDM symbols.

In a first approach, DL control signaling support for an MTC UE isprovided through CCHs having the same structure as C-CCHs but which,unlike C-CCHs, are transmitted only in a DL BW allocated to the MTC UEinstead of being transmitted over substantially the entire DL BW.

FIG. 11 is a diagram illustrating a multiplexing of CCHs, having a samestructure as C-CCHs, and PDSCHs for MTC UEs in OFDM symbols of a DLsubframe according to an embodiment of the present invention.

Referring to FIG. 11, a first two OFDM symbols available for DLsignaling to an MTC UE, as described in FIG. 10, are used fortransmissions of CCHs 1110. Remaining OFDM symbols of a DL subframe areused for transmissions of PDSCHs 1120. Transmissions of CCHs to the MTCUE span an entire DL BW 1130 allocated to the MTC UE.

A duration for transmitting CCHs to an MTC UE may be configured byhigher layer signaling and, unlike a configuration for conventional UEs,a respective PCFICH transmission in every subframe may be avoided. Thisis because due to a typically small DL BW, savings from dynamicallydimensioning in every subframe CCH resources for MTC UEs are largelyoffset by the resource overhead required for reliable PCFICH detectionby all MTC UEs in a same allocated DL BW.

Depending on a NodeB scheduler decision, PDSCH transmissions to MTC UEsmay span or may not span all DL BW allocated to MTC UEs. However, in thelatter case, DL BW not used for PDSCH transmissions to MTC UEs cannot beused in practice for PDSCH transmissions to conventional UEs as someOFDM symbols always contain CCH transmissions to MTC UEs. For example,it is likely in practice that most CCHs for MTC UEs schedule PUSCHtransmissions and most of the DL BW after transmissions of CCHs to MTCUEs remain unutilized.

In a second approach according to an embodiment of the present inventionthat avoids the above shortcoming associated with using the structure ofC-CCHs for transmitting CCHs to MTC UEs, the structure of E-CCHs is usedfor transmitting CCHs to MTC UEs. Although E-CCHs may also be used forconventional UEs, a different design is needed for MTC UEs due toaforementioned RF and DBB limitations.

FIG. 12 is a diagram illustrating a multiplexing of E-CCHs and PDSCHsfor MTC UEs according to an embodiment of the present invention.

Referring to FIG. 12, E-CCHs are transmitted to MTC UEs over allrespective OFDM symbols available for DL transmissions, as described inFIG. 10, and over two PRBs 1210A and 1210B (of a DL BW part allocated toMTC UEs) that are provided to respective MTC UEs through higher layersignaling. Remaining PRBs can be used for PDSCH transmissions 1220either to MTC UEs or to conventional UEs.

As a PRB granularity may be too large for PDSCH transmissions to MTCUEs, which typically convey small data packets or configuration controlinformation by higher layer signaling, a smaller granularity may be usedfor transmitting E-CCHs or PDSCHs to MTC UEs. For example, a minimumresource allocation unit can be half a PRB or equivalently a second PRBtype, which includes half the REs of a conventional PRB, can be used.The DMRS associated with each channel (E-CCH or PDSCH) can betransmitted over the whole PRB, such as illustrated in FIG. 6.Multiplexing PDSCHs to different MTC UEs in one PRB can also beperformed in the same manner. In this case, a UE may determine whichhalf of a PRB a respective PDSCH is transmitted, either by configurationfrom the network, or by explicit indication by one bit in a DL SA, or byimplicit indication (for example, depending on whether the UE isconfigured an odd or even RNTI). The DMRS antenna port associated with arespective MTC UE may be predetermined as configured to the MTC UE byhigher layer signaling or included in a field of a DCI format schedulingthe PDSCH reception.

FIG. 13 is a diagram illustrating a multiplexing of PDSCHs and E-CCHsusing a granularity of a half PRB according to an embodiment of thepresent invention.

Referring to FIG. 13, E-CCHs (or PDSCHs) are transmitted in two halfPRBs located at the two edges of a DL BW allocated to MTC UEs 1310A and1310B. The other half of each of the 2 PRBs containing transmissions ofE-CCHs is allocated to PDSCH transmissions to MTC UEs 1320A and 1320B.Remaining PRBs 1330 may be allocated for PDSCH transmissions to MTC UEsor to conventional UEs. As typically more UL data traffic than DL datatraffic is associated with MTC UEs, resources allocated to transmissionsof E-CCHs to MTC UEs may be similar to or more than resources allocatedto transmissions of PDSCHs to MTC UEs.

Multiplexing PUSCHs from different MTC UEs in one PRB can also beperformed in a similar manner as for PDSCHs and the associated UL DMRScan be transmitted in one PRB. The UL DMRS from different MTC UEs can beorthogonally multiplexed using different CS of a respective ZC sequencewhich may be predetermined as configured to the MTC UE by higher layersignaling or included in a field of a DCI format scheduling the PUSCHtransmission.

Due to their reduced DBB capabilities, MTC UEs may not support bothdistributed E-CCHs and localized E-CCHs while conventional UEs maysupport both E-CCH transmission types. A transmission type for an E-CCHcan be same as for a PDSCH and may depend on a RF capability of an MTCUE. If a DL BW supported by an MTC UE is small enough for transmissionsof DL signals to not experience significant frequency selectivity, adetection performance difference between a localized E-CCH and adistributed E-CCH will not be significant, as a channel responseexperienced by a respective transmission will be similar. Distributedtransmissions for both E-CCHs and PDSCH may offer interference diversitywhile leveraging on existing NodeB and UE implementations usingtransmitter antenna diversity.

Conversely, if a DL BW supported by an MTC UE is large enough fortransmissions of DL signals to experience significant frequencyselectivity, a detection performance difference between localized E-CCHsand distributed E-CCHs can be significant and depend on an availabilityof accurate, PRB-based, CSI at a NodeB. Then, localized PDSCH and E-CCHcan be precoded and the NodeB can select PRBs where an MTC UEexperiences large DL SINR. Considering an UL control overhead requiredfor a CSI feedback to track channel variations and provide sufficientaccuracy for beam-forming or Frequency Domain Scheduling (FDS) of PDSCHor E-CCH transmissions, localized PDSCH and E-CCH transmissions may bepractically feasible only for MTC UEs with very limited or no mobilityfor which infrequent CSI feedback suffices. Otherwise, if accuratePRB-based CSI for an MTC UE is not available at a NodeB, distributedtransmissions may substantially outperform localized transmissions.

When an E-CCH transmission to an MTC UE is distributed over multiplePRBs, two alternatives for a respective RS structure for demodulating acontrol signal in the E-CCH are described as follows.

A first alternative uses a CRS structure as shown in FIG. 1. However,unlike the CRS structure in FIG. 1, which is wideband and substantiallyoccupies an entire DL BW, a CRS used by an MTC UE may be contained onlyin a DL BW allocated to the MTC UE and may not extend in a remaining DLBW. Therefore, a CRS may be commonly used by MTC UEs but may not be usedby conventional UEs.

FIG. 14 is a diagram illustrating a CRS transmission only in a DL BWallocated to an MTC UE according to an embodiment of the presentinvention.

Referring to FIG. 14, which depicts an example corresponding to twoNodeB transmitter antenna ports, a CRS from a first antenna port 1410and a CRS from a second antenna port 1420 are transmitted in REs of a DLBW allocated to MTC UEs 1430 in same OFDM symbols as in FIG. 1. CRStransmissions may or may not occur in REs of a DL BW allocated toconventional UEs 1440A and 1440B.

If a PRB in a DL BW allocated to MTC UEs is not used for E-CCH or PDSCHtransmissions to MTC UEs, the PRB may be allocated to a PDSCHtransmission to a conventional UE. Then, if CRS is transmitted in REs ofthat PRB and if in respective OFDM symbols there are no CRStransmissions in a DL BW allocated to conventional UEs, a conventionalUE may not be aware of an existence of CRS and its PDSCH detection willbe degraded. This degradation can be avoided if MTC UEs assume presenceof CRS only in the PRB of a respective E-CCH or PDSCH transmission butthis will instead result to worse channel estimation for MTC UEs andassociated E-CCH or PDSCH performance degradation.

A second alternative uses a DMRS, which is transmitted only in PRBs usedby a respective E-CCH or PDSCH transmission. This avoids the abovetradeoff from using a CRS and allows flexible use of PRBs in a DL BWallocated to MTC UEs for transmissions to conventional UEs. To achievetransmit diversity, different precoding in different REs or differentPRBs may be used for the DMRS. However, prior to establishingcommunication with a NodeB, MTC UEs must detect a BCH, which may betransmitted by a NodeB using antenna transmitter diversity and receivedby MTC UEs based on CRS, MTC UEs should be able to perform channelestimation and demodulation based on both CRS and DMRS. Therefore, atradeoff for the RS structure used between the first alternative (CRS)and the second alternative (DMRS) is a receiver implementationsimplicity offered by the former versus a more efficient DL resourceutilization offered by the latter.

Another embodiment of the invention that considers reductions in controlsignaling overhead for MTC UEs is described as follows.

As sizes of data packets for MTC UEs are typically substantially smallerthan sizes of data packets for conventional UEs, and as a number of MTCUEs with PDSCH or PUSCH scheduling in a DL subframe may be greater thana respective number of conventional UEs, a relative control signalingoverhead associated with MTC UEs may become significant. For example,although a DCI format scheduling PDSCH or PUSCH to an MTC UE may addressa much smaller BW than a DCI format scheduling PDSCH or PUSCH to aconventional UE, a reduction in a DCI format size may not beproportional to a reduction in a BW size due to an existence of fieldswith fixed size such as the RNTI/CRC field. Also, it is not possible toreduce resources for transmitting HARQ-ACK signals conveying singlebinary information (ACK or NACK) regarding a reception of a data TB.

Therefore, if the same design principles as for conventional UEs arefollowed for MTC UEs, a control information size relative to a datainformation size can become significantly larger for MTC UEs than forconventional UEs leading to a proportionally much larger relativecontrol overhead for MTC UEs. A control signaling overhead for MTC UEsmay further increase if respective transmissions are constrained to beover a smaller BW than the BWs for conventional UEs. This constraintreduces frequency diversity or frequency scheduling gains therebynecessitating a use of more resources (time/frequency/power) in order tomaintain same detection reliability targets.

A reduction or avoidance of control signaling overhead associated withHARQ-ACK signal transmissions either from a NodeB or from an MTC UE inresponse to, respectively, detections of data TBs in a PUSCH or a PDSCHis subsequently considered.

For a dynamically scheduled PUSCH, assuming than an MTC UE keepsreceived data for a HARQ process in its buffer until a respective NDIbit is toggled, an NDI field in a corresponding DCI format avoids a needfor explicit HARQ-ACK signaling. For semi-persistently scheduled (SPS)PUSCH, associated applications are typically related to file transfers,which are delay tolerant. Then, a higher layer ARQ, such as a Radio LinkControl (RLC) ARQ, is sufficient to trigger a retransmission whenever aPUSCH is not correctly received. A network may also avoid a latencyassociated with higher layer ARQ by dynamically scheduling a PUSCHretransmission, for example, when an overhead for transmitting anassociated DCI format is not a concern, such as during off-peak hours,for example. Therefore, the NDI field can be preserved in DCI formatsscheduling PUSCH to provide HARQ-ACK information and explicit HARQ-ACKsignaling to MTC UEs through respective PHICHs may not be supported.

PDSCH transmissions to MTC UEs are typically used for configuration oftransmission parameters and to provide respective control information byhigher layers. Therefore, PDSCH transmissions are not as frequent asPUSCH transmissions from MTC UEs and do not consume as many resources.Such transmissions enable a network to target a more reliable PDSCH thanPUSCH reception. A network may also derive whether a PDSCH was correctlyor incorrectly received by monitoring a response from an MTC UE to theconfiguration information. For example, if a PDSCH configures an SRStransmission from an MTC UE, a network may detect a presence or absenceof an SRS transmission with configured parameters and determine that theMTC UE correctly or incorrectly, respectively, received the PDSCH.Additionally, if a network schedules both a PDSCH and a PUSCH to an MTCUE in a same subframe, as can be expected in practice due to UE dominanttraffic for MTC UEs, the MTC UE can include HARQ-ACK information for thePDSCH reception in the PUSCH transmission. Therefore, in addition tohigher layer ARQ, sufficient means exist for a NodeB to obtaininformation of whether an MTC UE correctly or incorrectly received aPDSCH and therefore separate transmission of a HARQ-ACK signal from anMTC UE is not needed. This also avoids the need to include TPC commandsfor HARQ-ACK signal transmission in a PUCCH in DCI formats schedulingPDSCH.

Therefore, embodiments of present the invention consider that physicallayer retransmissions for an HARQ process are supported for MTC UEs butonly through a use of a NDI field when using a PUSCH transmission or byincluding HARQ-ACK information in a PUSCH when using a PDSCHtransmission and the respective DCI formats are accordingly designed.Benefits from avoiding explicit support of HARQ-ACK signal transmissionsin response to a PDSCH or to a PUSCH detection include an associatedcontrol signaling overhead reduction, avoidance of resourcefragmentation, a simpler system design, and a reduced DBB designcomplexity for MTC UEs.

Another embodiment of the invention that considers the design ofdifferent functionalities for signal transmissions to or from MTC UEscompared to conventional UEs is described as follows.

A first functionality that needs to be modified for MTC UEs compared toconventional UEs is CSI reporting. Conventional UEs compute a widebandCQI based on an unrestricted observation interval in time and frequencyand derive for each CQI value a CQI index between 1 and 15 for which asingle PDSCH TB with a combination of modulation scheme and TB sizecorresponding to the CQI index, and occupying a group of DL PRBs couldbe received with a TB error probability not exceeding 0.1. If this isnot possible, a CQI index of 0 is reported by the conventional UE. Aninterpretation of the CQI indices is given in Table 1.

TABLE 1 4-bit CQI Table CQI CQI code rate x Bits index Modulation 1024efficiency 0000  0 out of range 0001  1 QPSK  78 0.1523 0010  2 QPSK 1200.2344 0011  3 QPSK 193 0.3770 0100  4 QPSK 308 0.6016 0101  5 QPSK 4490.8770 0110  6 QPSK 602 1.1758 0111  7 16 QAM 378 1.4766 1000  8 16 QAM490 1.9141 1001  9 16 QAM 616 2.4063 1010 10 64 QAM 466 2.7305 1011 1164 QAM 567 3.3223 1100 12 64 QAM 666 3.9023 1101 13 64 QAM 772 4.52341110 14 64 QAM 873 5.1152 1111 15 64 QAM 948 5.5547

As MTC UEs need to have reduced DBB cost and capabilities, MTC UEs maysupport only QPSK modulation for data transmitted in a PDSCH TB.Therefore, only the first 7 CQI indices in Table 1 are applicable towideband CQI reporting from MTC UEs. Alternatively, a larger granularityfor a spectral efficiency may be supported and only 8 of the 16 valuesin Table 1 may be indicated. Then, a respective 3-bit CQI table is givenin Table 2 (assuming use of only QPSK modulation—a similar table can beconstructed if only every other efficiency from Table 1 is reported).Moreover, as MTC UEs receive PDSCH only in an allocated DL BW, which canbe less than a total DL BW available to conventional UEs, CQI reportingfor MTC UEs should be restricted in frequency only in the allocated DLBW.

TABLE 2 3-bit CQI Table CQI CQI code Bits index Modulation rate x 1024efficiency 000 0 out of range 001 1 QPSK  78 0.1523 010 2 QPSK 1200.2344 011 3 QPSK 193 0.3770 100 4 QPSK 308 0.6016 101 5 QPSK 449 0.8770110 6 QPSK 602 1.1758 111 7 QPSK reserved reserved

Additional differences in CQI reporting functionalities betweenconventional UEs and MTC UEs can include reporting support of sub-bandCQI, PMI, and RI. As a conventional UE can receive PDSCH at any part ofa total DL BW, CQI reporting corresponding to sub-bands of the total DLBW may be configured in order to enable FDS. Conversely, because MTC UEscan receive PDSCH only in a small DL BW, support of sub-band CQI is notneeded.

A conventional UE may also support PDSCH spatial multiplexing andreception of large data TBs and report a support of a PDSCH transmissionrank larger than one if it experiences favorable DL channel conditions.Conversely, as, according to the present embodiment of the presentinvention, MTC UEs do not support PDSCH spatial multiplexing andreceived data TBs are typically small, there is no need for a PDSCHtransmission rank reporting from MTC UEs.

For CRS-based PDSCH and CCH demodulation at MTC UEs, respectivetransmissions are not precoded and, therefore, there is no need for MTCUEs to report PMI.

For DMRS-based PDSCH and CCH demodulation at an MTC UE and an FDDsystem, respective transmissions may be precoded and the MTC UE mayreport a PMI to enable non-random precoding of a signal from a NodeB.For DMRS-based PDSCH and CCH demodulation at an MTC UE and a TDD system,respective transmissions may be precoded but, due to the reciprocity ofthe DL and UL channels, an MTC UE does not need to report a PMI toenable precoding of a signal from a NodeB since this information isobtained by the NodeB through a DMRS or SRS transmission by the MTC UE.

When an MTC UE reports only a wideband CQI of 3 bits, a required SINR toachieve a target detection reliability is significantly decreasedcompared to a respective one for a CSI of 4-11 bits that may includewideband CQI, sub-band CQI, and PMI. This SINR reduction can beexploited to reduce an associated PUCCH overhead by increasing amultiplexing capacity of MTC UEs per PRB.

One approach to increase (double) a multiplexing capacity of periodicCQI transmissions for MTC UEs is to allow transmission of periodic CQIover one slot instead of over one subframe. A duration of a periodic CQItransmission (slot or subframe) can be configured to an MTC UE by aNodeB through higher layer signaling (in addition to parameters such asa PUCCH RB, the CS for a ZC sequence, a transmission period, etc.). MTCUEs that are not UL-coverage-limited can be configured to transmit inone slot of a PUCCH subframe. A performance degradation compared to aconventional periodic CSI structure will include a 3 decibel (dB) loss,due to reducing a transmission time interval by a factor of 2, and afrequency diversity loss due to limiting a transmission in samefrequency resources. However, a 3 dB loss can be tolerable, due to asmaller periodic CQI information payload for MTC UEs compared toconventional UEs (3 bits instead of 4-to-11 bits), while a frequencydiversity loss will typically be small, if a smaller UL BW is allocatedto MTC UEs, and will be further reduced due to receiver antennadiversity that typically exists at a NodeB.

FIG. 15 is a diagram illustrating a first approach to increase amultiplexing capacity of periodic CQI transmissions from MTC UEsaccording to an embodiment of the present invention.

Referring to FIG. 15 and for PUCCH transmissions over one RB, a set of Kconventional UEs transmit periodic CQI reports by multiplexing theirtransmissions in a first slot 1510 and in a second slot 1520 of a PUCCHsubframe using respectively K different CS of a ZC sequence. A first setof K MTC UEs transmit periodic CQI reports by multiplexing theirtransmissions in a first slot 1530 of a PUCCH subframe usingrespectively K different CS of a ZC sequence and a second set of K MTCUEs transmit periodic CQI reports by multiplexing their transmissions ina second slot 1540 of a PUCCH subframe using respectively K different CSof a ZC sequence. Therefore, a multiplexing capacity for MTC UEs istwice the multiplexing capacity of conventional UEs.

Another approach to increase (double) a multiplexing capacity ofperiodic CQI transmissions for MTC UEs is to restrict such transmissionsto a half RB, instead of one RB for conventional UEs, and use ZCsequences of a half-length compared to ZC sequences used by conventionalUEs. For example, for a RB including REs, two ZC sequences of length 6(which can be the same), can be used for transmitting periodic CQI byMTC UEs in two half RBs while ZC sequences used for transmittingperiodic CQI by conventional UEs are of length 12 and periodic CQItransmission is in one RB. Through this allocation, frequency diversityloss is avoided, and only an SINR loss of 3 dB exists for periodic CQItransmissions from MTC UEs compared to SINR losses from conventionalUEs.

FIG. 16 is a diagram illustrating a second approach to increase amultiplexing capacity of periodic CSI transmissions from MTC UEsaccording to an embodiment of the present invention.

Referring to FIG. 16, a set of K conventional UEs transmit periodic CQIreports by multiplexing their transmissions over a RB in a first slot1610 and in a second slot 1620 of a PUCCH subframe using respectively Kdifferent CS of a ZC sequence. A first set of K MTC UEs transmitperiodic CQI reports by multiplexing their transmissions over half RB ina first slot 1630A and in a second slot 1630B of a PUCCH subframe usingrespectively K different CS of a ZC sequence and a second set of K MTCUEs transmit periodic CQI reports by multiplexing their transmissionsover half RB in a first slot 1640A and in a second slot 1640B of a PUCCHsubframe using respectively K different CS of a ZC sequence.

Another approach to increase a multiplexing capacity of periodic CQItransmissions for MTC UEs is to further reduce a number of bits forwideband CQI reports from 3 to 2 and report 4, instead of 7, CQIindexes. For example, reported indexes can be as in Table 3 (or byreporting every fourth of the 16 efficiencies in Table 1). A drawback ofthis approach is that there will be some loss in the spectral efficiencyof PDSCH transmissions, because a granularity of wideband CQI reports isincreased. However, as for typical DL SINR distributions, most MTC UEsare able to support a largest spectral efficiency for QPSK modulationthat is still reported (this largest spectral efficiency captures allother ones corresponding to the use of QAM16 or QAM64 in Table 1 whichare not applicable for MTC UEs), and therefore, a loss in spectralefficiency will be small.

An advantage of this approach is that, in addition to increasedreliability of CQI feedback as a number of bits is decreased to 2, aPUCCH format used by conventional UEs for transmitting 2 HARQ-ACK bitscan be used by MTC UEs for CQI reporting according to embodiments of thepresent invention, thereby increasing a multiplexing capacity by as muchas a factor of 3, and also reducing UL overhead. Moreover, a singlePUCCH structure can be used by MTC UEs to support HARQ-ACKtransmissions, if necessary, as well as to support SR transmissions. Ifa UE is to transmit a CQI report in a same subframe as a HARQ-ACKsignal, the UE can suspend transmission of the CQI report and transmitonly the HARQ-ACK signal. Additionally, CQI feedback may have a nestedstructure with a first CQI reporting indicating a first value, as forexample in Table 3, and a second CQI reporting indicating a second valuethat includes predetermined values around the first value. For example,the first CQI reporting (including 2 bits) may indicate a value of0.6016 and the second CQI reporting (including 1 bit or 2 bits) mayindicate one of the 0.3770 or 0.6016 values.

TABLE 3 2-bit CQI Table CQI code Bits CQI index Modulation rate x 1024efficiency 00 0 out of range 01 1 QPSK 120 0.2344 10 2 QPSK 308 0.601611 3 QPSK 602 1.1758

FIG. 17 is a diagram illustrating a third approach for increasing amultiplexing capacity of periodic CSI transmissions for MTC UEsaccording to an embodiment of the present invention.

Referring to FIG. 17, a set of K₁ MTC UEs transmit periodic CQI reportsby multiplexing the CQI bits 1710 with a ZC sequence 1720 and alsotransmitting an non-modulated ZC sequence for RS 1730 using the samestructure per slot 1740 as conventional UEs use for HARQ-ACK signaltransmissions.

A second functionality that needs to be modified for MTC UEs accordingto embodiments of the present invention compared to conventional UEs isthe one of SRS transmissions that is not configured with a maximum SRSBW and hop in successive transmission instances in different BWs withinthe maximum SRS BW. Conventional UEs that are not configured, due to lowSINR or due to overhead considerations, to transmit a SRS with a maximumBW can be configured by a NodeB to transmit SRS with a smaller BW andwith location that is hopping within a maximum SRS BW over successiveSRS transmission instances in order to scan in this way a maximum SRSBW.

SRS transmissions according to embodiments of the present invention mayalso be supported by an MTC UE in order to assist a network to determinean appropriate UL BW for PUSCH transmissions, for example by selectingan UL BW from a predetermined set of UL BWs where the MTC UE experiencesfavorable SINR for a signal transmission. The set of possible BWs, issignaled to the MTC UE by a NodeB through higher layer signaling. Forexample, to minimize UL BW fragmentation experienced for PUSCHtransmissions by conventional UEs due to an allocation of UL BWs to MTCUEs, a number of possible UL BWs for an MTC UE may be limited towardsthe two edges of a total UL BW available for PUSCH transmissions.Therefore, it is inefficient for an MTC UE to transmit SRS in all BWparts of a maximum SRS BW configured for conventional UEs as these BWparts may not be allocated to the MTC UE.

Consequently, a modification to an SRS hopping pattern used by aconventional UE can be used for an MTC UE in order to include only ULBWs that a network may allocate to the MTC UE. A resulting modified SRShopping pattern is described in U.S. patent application Ser. No.12/986,620 titled “Enhancing Features of Uplink Reference Signals”. Whenan SRS transmission is activated by a DCI format, an SRS transmission BWindicated by the DCI format can only belong to a predetermined set of ULBWs.

FIG. 18 is a diagram illustrating a process for an MTC UE to perform SRStransmissions according to an embodiment of the present invention.

Referring to FIG. 18, an MTC UE is first informed by a NodeB, throughhigher layer signaling, of a set of UL BWs 1810. For example, a UL BW of48 RBs can be divided into 8 BW parts of 6 RBs each, and a respectivebit-map of 8 bits can indicate, to an MTC UE, the BW parts for an SRStransmission (for example, a binary 1 may indicate a BW part for SRStransmission and a binary 0 may indicate a BW part excluded from an SRStransmission). The MTC UE is also informed of a set of SRS transmissionparameters, such as the SRS transmission BW, the SRS transmissionperiod, and other parameters associated with the construction of theSRS, which can also be based on a ZC sequence 1820. The MTC UE transmitsan SRS at each respective transmission instance only within a BW in theset of indicated UL BWs 1830 (the SRS transmission BW may notnecessarily be the same as each UL BW in the set of UL BWs).

Due to RF re-tuning time requirements, which are typically in the rangeof a few transmission symbol intervals, it is not practically possiblefor an MTC UE to transmit in a same subframe control or data signalswithin one BW and SRS within another BW, if the transmission of controlor data signals and the transmission of an SRS happen to coincide in thesame subframe and be in different UL BWs. Therefore, in such a case,according to an embodiment of the present invention, an MTC UE suspendsan SRS transmission and performs only transmission of control or datasignals.

Although embodiments of the present invention described herein aboverefer to transmissions of control signals and data signals from an MTCUE within a same allocated BW, embodiments of the present invention arenot limited to these examples, and transmission of control signals maybe within a different allocated BW than transmission of data signals inaccordance with embodiments of the present invention. A network may thenconfigure an MTC UE to transmit a PUSCH within a first set of RBs andtransmit a PUCCH within a second set of RBs. An MTC UE can tune its RFat an appropriate set of RBs and when the MTC UE needs to transmit bothUCI and data information, the MTC UE can multiplex both in a PUSCH. Onereason for configuring an MTC UE different sets of RBs for transmissionsof control signals and data signals is to avoid congestion when MTC UEsare allocated several, common, RBs for PUCCH transmissions, since PUCCHmultiplexing capacity per RB (up to 18 or 36 UEs) can be much largerthan PUSCH multiplexing capacity per RB (typically only in the order ofone UE). Another reason is to provide flexibility to a network inreserving a set of RBs for PUCCH transmissions by MTC UEs and utilize ornot utilize another set of RBs for PUSCH transmissions by MTC UEs whilealso considering scheduling of conventional UEs.

Additionally, although embodiments of the present invention describedherein above refer to MTC UEs completing the initial communication setupin a subset of the PRBs used for BCH transmission, such as for examplethe middle six PRBs in a DL BW, prior to being informed by higher layersignaling of another allocated DL BW, embodiments of the presentinvention are not necessarily be the case in practice. For example, inorder to support communication in heterogeneous networks, interferencecoordination among different cells is needed for PDCCH transmissionsthat schedule, to MTC UEs, the reception of PDSCHs that provide initialconfiguration information and are less reliable than BCH transmissions.

A first alternative is for an MTC UE to implicitly derive a DL BW forcommunication after BCH detection and prior to detecting PDCCHs andrespective PDSCHs conveying a higher layer control signaling thatallocates a DL BW and other parameters for subsequent communication as afunction of a NodeB (cell) identity that is provided by synchronizationsignals. For example, if a result of a modulo operation between a cellidentity and a predetermined number (such as a subframe number) is zero,a first DL BW is used for subsequent DL communication for MTC UEs afterBCH reception; otherwise, a second DL BW is used.

A second alternative is for an MTC UE to derive PRBs for communicationafter BCH detection to be a subset of the BCH PRBs based again on a cellidentity. For example, if a result of a modulo operation between a cellidentity and a predetermined number is zero, a first half of PRBs of BCHtransmission is used for subsequent PDCCH and PDSCH transmissions;otherwise, a second half of PRBs of BCH transmission is used.

FIG. 19 is a diagram illustrating a DL BW determination by an MTC UEafter BCH detection according to an embodiment of the present invention.

Referring to FIG. 19, an MTC UE first detects synchronization signalsand the BCH and determines an identity of a respective cell 1910. Basedon an outcome of a modulo operation between a cell identity and apredetermined number L 1920, the MTC UE determines a first DL BW forcommunication after BCH detection 1930 or a second DL BW forcommunication after BCH detection 1940. Although the method of FIG. 19is performed according to the first of the previous two alternativesdescribed herein above, extension of the method of FIG. 19 to the secondof the previous alternatives is straightforward. Alternatively, the DLBW for communication after BCH detection may be indicated by the BCH.

Finally, as scheduling of PDSCH or PUSCH transmissions to or from an MTCUE, respectively, may not be needed in every subframe, as theapplications for the MTC UE may not have strict latency requirements,the subframes possible for scheduling PDSCH or PUSCH to the MTC UE canbe indicated from the NodeB through higher layer signaling. For example,a network may signal to an MTC UE a bit-map including X bits indicatingrespective X subframes where the network may transmit a DL SA or an ULSA to an MTC UE (for example, for binary ‘1’ value) and subframes wherethe MTC UE may not transmit a DL SA or an UL SA to the MTC UE (forexample, for binary ‘1’ value). The set of X subframes may be determinedwith respect to a reference subframe such as for example the firstsubframe in a reference radio frame including multiple subframes. Thisapproach can increase the instances where an MTC UE does not need totransmit or receive, thereby increasing the associated power savings.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for receiving downlink controlinformation by a user equipment, the method comprising: receiving, froma base station, higher layer signaling comprising a bit-map consistingof a plurality of bits indicating respective transmission time intervals(TTIs) where the base station is capable of transmitting a physicaldownlink control channel (PDCCH) and the base station is not capable oftransmitting a PDCCH; identifying at least one TTI to monitor at leastone candidate PDCCH in at least one search space; decoding the at leastone candidate PDCCH in the identified at least one TTI for obtaining thedownlink control information; determining one or more sub-carrierscorresponding to a wideband reference signal from a set of sub-carriersfor data reception; and receiving downlink data on sub-carriersexcluding the determined one or more sub-carriers, wherein eachcandidate PDCCH is demodulated using a demodulation reference signalthat is received only inside a reception bandwidth of the candidatePDCCH.
 2. The method of claim 1, wherein the user equipment isconfigured to be able to perform channel estimation and demodulation ofthe candidate PDCCH based on both of the demodulation reference signaland a wideband reference signal that is received within a widebandincluding the reception bandwidth of the candidate PDCCH.
 3. The methodof claim 1, further comprising: receiving a broadcast channel during aninitial access process; determining a reception bandwidth for a set ofcandidate PDCCHs based on information in the broadcast channel;receiving the candidate PDCCH over a bandwidth that is a subset of thereception bandwidth for the set of candidate PDCCHs; and receiving awideband reference signal for demodulating the candidate PDCCH over thereception bandwidth for the set of candidate PDCCHs.
 4. An apparatus ofa user equipment for receiving downlink control information, theapparatus comprising: a receiver configured to receive, from a basestation, higher layer signaling comprising a bit-map consisting of aplurality of bits indicating respective transmission time intervals(TTIs) where the base station is capable of transmitting a physicaldownlink control channel (PDCCH) and the base station is not capable oftransmitting a PDCCH; and a processor configured to: identify at leastone TTI to monitor at least one candidate PDCCH in at least one searchspace, decode the at least one candidate PDCCH in the identified atleast one TTI for obtaining the downlink control information, determineone or more sub-carriers corresponding to a wideband reference signalfrom a set of sub-carriers for data reception, and control the receiverto receive downlink data on sub-carriers excluding the determined one ormore sub-carriers, wherein each candidate PDCCH is demodulated using ademodulation reference signal that is received only inside a receptionbandwidth of the candidate PDCCH.
 5. The apparatus of claim 4, whereinthe processor is configured to be able to perform channel estimation anddemodulation of the candidate PDCCH based on both of the demodulationreference signal and a wideband reference signal that is received withina wideband including the reception bandwidth of the candidate PDCCH. 6.The apparatus of claim 4, wherein, the processor is further configuredto determine a reception bandwidth for a set of candidate PDCCHs basedon information in a broadcast channel received during an initial accessprocess, and the receiver is further configured to: receive thecandidate PDCCH over a bandwidth that is a subset of the receptionbandwidth for the set of candidate PDCCHs, and receive a widebandreference signal for demodulating the candidate PDCCH over the receptionbandwidth for the set of candidate PDCCHs.
 7. A method for transmittingdownlink control information, the method comprising: transmitting, to auser equipment, higher layer signaling comprising a bit-map consistingof a plurality of bits indicating respective transmission time intervals(TTIs) where the base station is capable of transmitting a physicaldownlink control channel (PDCCH) and the base station is not capable oftransmitting a PDCCH; identifying at least one TTI in which the userequipment monitors a set of candidate PDCCHs in at least one searchspace; transmitting downlink control information on a candidate PDCCH ofthe set of candidate PDCCHs in the identified at least one TTI;determining one or more sub-carriers corresponding to a widebandreference signal from a set of sub-carriers for data reception; andtransmitting downlink data on sub-carriers excluding the determined oneor more sub-carriers, wherein each candidate PDCCH is demodulated at theuser equipment, using a demodulation reference signal that is receivedonly inside a reception bandwidth of the candidate PDCCH.
 8. The methodof claim 7, wherein the user equipment is configured to be able toperform channel estimation and demodulation of the candidate PDCCH basedon both of the demodulation reference signal and a wideband referencesignal that is received within a wideband including the receptionbandwidth of the candidate PDCCH.
 9. The method of claim 7, furthercomprising: transmitting a broadcast channel during an initial accessprocess, wherein the broadcast channel comprises information on areception bandwidth for the set of candidate PDCCHs; transmitting thecandidate PDCCH over a bandwidth that is a subset of the receptionbandwidth for the set of candidate PDCCHs; and transmitting a widebandreference signal for demodulating the candidate PDCCH over the receptionbandwidth for the set of candidate PDCCHs.
 10. An apparatus of a basestation for transmitting downlink control, the apparatus comprising: atransmitter configured to transmit, to a user equipment, higher layersignaling information comprising a bit-map consisting of a plurality ofbits indicating respective transmission time intervals (TTIs) where thebase station is capable of transmitting a physical downlink controlchannel (PDCCH) and the base station is not capable of transmitting aPDCCH; and a processor configured to: identify at least one TTI in whichthe user equipment monitors a set of candidate PDCCHs in at least onesearch space, control the transmitter to transmit downlink controlinformation on a candidate PDCCH of the set of candidate PDCCHs in theidentified at least one TTI, determine one or more sub-carrierscorresponding to a wideband reference signal from a set of sub-carriersfor data reception, and control the transmitter to transmit downlinkdata on sub-carriers excluding the determined one or more sub-carriers,wherein each candidate PDCCH is demodulated at the user equipment, usinga demodulation reference signal that is received only inside a receptionbandwidth of the candidate PDCCH.
 11. The apparatus of claim 10, whereinthe user equipment is configured to be able to perform channelestimation and demodulation of the candidate PDCCH based on both of thedemodulation reference signal and a wideband reference signal that isreceived within a wideband including the reception bandwidth of thecandidate PDCCH.
 12. The apparatus of claim 10, wherein the transmitteris further configured to: transmit a broadcast channel during an initialaccess process, wherein the broadcast channel comprises information on areception bandwidth for the set of candidate PDCCHs; transmit thecandidate PDCCH over a bandwidth that is a subset of the receptionbandwidth for the set of candidate PDCCHs; and transmit a widebandreference signal for demodulating the candidate PDCCH over the receptionbandwidth for the set of candidate PDCCHs.